Regulation of polyphase furnaces.



R. FLEMING.

REGULATION OF POLYPHASB FURNACES. APPLICATION TILED FEB. 13, 1908.

904,194. Patented Nov. 17, 1908 Witnesses: Inventor:

Richard Fleming, ,V 2 I 2 9 6Z5 by full.

'interio UNITED STATES PATENT OFFICE.

RICHARD FLEllIING, OF LYNN, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

- I REGULATION OF'POLYPHASE FURNACES.

Specification of Letters Patent.

Patented Nov. 1'7, 1908.

App1ieatiiin filed February 1a, 1908. Serial No. 415,768.

. assachusetts, have invented certain new, and useful Improvements 1n. Regulatlon for a Polyphase. Furnace, of which the following is a specification.

My invention relates to the operation of an electric furnace supplied with a polyphase alternating current, and comprises means for measuring the voltage between the electrodes and an inaccessible neutral. point within the furnace, and thus provides a basis for the regulation of said electrodes.

When a star-connected pholyphase current, for example, three-phase current, is supplied to an electric furnace, which may be either an are or a resistance furnace, it is convenient to base the regulation of the electrodes upon the resistance between each electrode and a neutral point within the furnace. In the case of a resistance furnace, as an electrode is worn away, and its distance from the neutral point increases, the .resist ance offered to the current increases. When such a star-connected circuit is connected to a transformer delivering constant current, an unbalancing of the load by such change of resistance results in the unbalancing of the current in the system. In the case of an arc furnace it is convenient to maintain and regulate the length of the arcs by observing the drop infvoltage from the electrodes to the bath.

An additional electrode has heretofore been placed within the furnace and connected by a metallic conductor to the-compath. As this interior electrode is subjected to-jthe intense heat and the chemical activity of -the-chargavit is very troublesome, requiring frequent renewals.

By establishing an artificial neutral 'outside of the furnace, which will be a counterr -i mage,-- of" the interior neutral point, pense with the additional A voltmeter My invention will best be understood by reference to the following description taken in connection with the accompanying draw- %he novel features. of my invention are pointed out with. particularity in the appended claims.

The drawin shows diagrammatically va cross-section of the electric furnace 1,-with electrodes "2, 3, 4 connected to a source of three-phase alternating current in mains 5,

6, 7, which are'connected to some source of currentwith a star-winding, such as a transformer having an endof its coils connected kept approximately constant with a suitable voltage regulator.

' Although a three-phase circuit hasbeen shown for illustration, it is obvious that any other polyphase circuit might have been shown. To each of the electrodes is connected a reactance coil, as coils 8, 9, 10, which are joined at a common point, 11. This point 11 then forms a neutral with reference to the, three-phase current in the system. The current flowing through these reactancesma'y be made as small as desired by increasing the number of turns. It will normally be equal in each coil, but suppose the resistance from the electrode 2, to the char e say, I y wearing away of the electrode, an unbalancing of the load current would result. This unbala'ncing would result in increase of current flowing through the reactance coil 10, thusunbalancing the current in the reactances. would, of course, result in changeof voltage across each coil. voltmeter across each coil, as meters 12, 13, 14:, a change of resistance for any cause whatever within the furnace would announce itself by a deflection of the voltmeters. In the case of an increase of resistance by a shortening of the electrode 2, as above described, an increase of voltage would result across the mam 5 and neutral 11, thus causing a deflection of the voltmeter 14.

What I claim as new and desire to secure by Letters Patent of the United States, is,

l. The combination of a polyphase electric furnace, a source of alternating current, an

This state of affairs Therefore, by placing a uring changes of potential between said arartificial neutral point, and means for measand voltmeters in parallel with said reactances.

In Witness whereof, I have hereunto set my hand this seventh day of- February, 1908.

RICHARD FLEMING.

tificial neutral and any of said electrodes.

2. The combination of a polyphase electric furnace, a source of alternating current of substantially constant voltage reactances connected at one end to said electrodes and at the other end to a common neutral point,

itnesses JOHN A. McMANUs, Jr., HENRY O. WESTENDARI'. 

